Auto merge of #139018 - oli-obk:incremental-trait-impls, r=compiler-errors

Various local trait item iteration cleanups

Adding a trait impl for `Foo` unconditionally affected all queries that are interested in a completely independent trait `Bar`. Perf has no effect on this. We probably don't have a good perf test for this tho.

r? `@compiler-errors`

I am unsure about https://github.com/rust-lang/rust/pull/139018/commits/9d05efb66f7b599eeacb5d2456f844fe4768e865 as it doesn't improve anything wrt incremental, because we still do all the checks for valid `Drop` impls, which subsequently will still invoke many queries and basically keep the depgraph the same.

I want to do

https://github.com/rust-lang/rust/blob/9549077a47099dc826039c051b528d1013740e6f/compiler/rustc_middle/src/ty/trait_def.rs#L141

but would leave that to a follow-up PR, this one changes enough things as it is

1 files changed, 7 insertions, 3 deletions

diff --git a/compiler/rustc_mir_transform/src/check_const_item_mutation.rs b/compiler/rustc_mir_transform/src/check_const_item_mutation.rs
index ceea72c6755..375db17fb73 100644
--- a/compiler/rustc_mir_transform/src/check_const_item_mutation.rs
+++ b/compiler/rustc_mir_transform/src/check_const_item_mutation.rs
@@ -53,9 +53,13 @@ impl<'tcx> ConstMutationChecker<'_, 'tcx> {
         //
         //     #[const_mutation_allowed]
         //     pub const LOG: Log = Log { msg: "" };
-        match self.tcx.calculate_dtor(def_id, |_, _| Ok(())) {
-            Some(_) => None,
-            None => Some(def_id),
+        // FIXME: this should not be checking for `Drop` impls,
+        // but whether it or any field has a Drop impl (`needs_drop`)
+        // as fields' Drop impls may make this observable, too.
+        match self.tcx.type_of(def_id).skip_binder().ty_adt_def().map(|adt| adt.has_dtor(self.tcx))
+        {
+            Some(true) => None,
+            Some(false) | None => Some(def_id),
         }
     }